Measurement of dust resistivity and back corona in electrostatic precipitators

Transkript

1 Measurement of dust resistivity and back corona in electrostatic precipitators D. Pieloth, M. Majid, H. Wiggers, P.Walzel PiKo Workshop Universität Bremen / Fakultät Bio- & Chemieingenieurwesen Mechanische Verfahrenstechnik

2 Outline Motivation ElectroStatic Precipitators (ESP) Dust resistivity Back corona and the collection efficiency of electrostatic precipitators Dust resistivity measurement Experimental setup New measurement chamber Particle diameter and dust resistivity Design Measurement program Summary and Outlook 2

3 Electrostatic precipitator Dust deposition pattern within an electrostatic precipitator 3

4 Dust resistivity Decrease of E-Field strength in electrostatic participator due to voltage drop within the dust layer I = electric current ρ = resistivity s = layer thickness A = area of collecting electrode j = current density Mean E-Field strength within the dust layer: Back discharge of already absorbed dust particles Back corona due to overriding the E-Field strength within the dust layer Drop of collection efficiency of electrostatic precipitators 4

5 Dust resistivity and the collection efficiency of electrostatic precipitators Definition of dust resistivity ρ: R = resistance (Ohm s law: I = U/R) s = layer thickness A = area of collecting electrode ρ = dust resistivity Influence of resistivity ρ on collection efficiency of electrostatic precipitators e.g. migration velocity Source: Weber/Brocke -> increase of resistivity ρ -> drop of migration velocity -> collection efficiency decreases 5

6 Measurement of dust resistivity Experimental setup 6

7 Measurement of dust resistivity Electrode arrangement 7

8 Back discharge of already separated dust particles due to air flow Dust collecting plate within an electrode of an electrostatic precipitator Adhesion of the upper dust layer within E-Field? Influence of current density, dust properties, gas conditions? 8

9 Particle diameter and dust resistivity Particles used in dust resistivity measurement (scanning electron microscope pictures) 9

10 Particle diameter and dust resistivity Particles used in dust resistivity measurement (scanning electron microscope pictures) 10

11 Particle diameter and dust resistivity 11

12 Particle diameter and dust resistivity 12

13 Particle diameter and dust resistivity 13

14 Particle diameter and dust resistivity 14

15 New dust resistivity measurement chamber Design aims max. air temperature 500º C stainless steel defined dust layer thickness better visibility of processes within chamber lower heat loss adhesion of dust (gas stream velocities) new measurement chamber 15

16 New dust resistivity measurement chamber 16

17 Schematic of new dust resistivity measurement chamber adhesion of dust (different gas stream velocities will be applied) 17

18 New dust resistivity measurement chamber Measurement program Detection of particle morphology effects on resistivity ρ and back corona under defined air conditions (Glass, γ-al 2 O 3, Limestone) Experiments with dust layers collected with collecting plate during operation of an electrostatic precipitator (electrostatic precipitator, TU Dortmund) Adhesion of dust particles on top layer of dust, detection of release of those particles into gas stream (Laser beam experiments) 18

19 Summary and Outlook Infrastructure for dust resistivity measurement in place (experience, measurement methods, electrostatic participator) First results for dust resistivity measurement (dust particle diameter, air conditions) Construction of new dust resistivity measurement chamber almost finished Measurement program with new measurement chamber will start soon Vielen Dank for the financial support by Thank you for your attention! 19